Sinus tarsi syndrome is a painful, often function?limiting condition of the lateral hindfoot caused by inflammation, injury, or instability within the sinus tarsi—the small canal between the talus and calcaneus. It most commonly follows ankle sprains and presents with lateral ankle pain, swelling, and instability.

Overview and Anatomical Context

The sinus tarsi is a cone?shaped cavity on the lateral side of the foot, forming part of the subtalar joint, which allows inversion and eversion. It contains fat, ligaments (including the interosseous talocalcaneal ligament), blood vessels, and nerve endings. When these structures become irritated, inflamed, or damaged, sinus tarsi syndrome (STS) develops.

The space is small and pressure?sensitive; even mild swelling can produce significant pain. STS is often underdiagnosed because its symptoms overlap with other lateral ankle conditions.

Etiology

Most cases of STS arise from inversion ankle sprains, which account for 70–80% of cases. These sprains can injure the subtalar ligaments, leading to chronic instability and inflammation.

Other causes include:

• Recurrent ankle sprains — repeated trauma leads to scar tissue and synovitis.
• Foot pronation or flatfoot deformity — increases compression in the sinus tarsi.
• Chronic ankle instability — subtalar joint instability is strongly associated with STS.
• Inflammatory arthropathies — rheumatoid arthritis, gout, and ankylosing arthritis can inflame the subtalar joint.
• Overuse — high?impact sports, trail running, and activities requiring rapid cutting or pivoting.
• Posterior tibial tendon dysfunction — alters hindfoot alignment and increases sinus tarsi load.

Clinical Presentation

Patients typically report:

• Lateral ankle pain—a constant ache that becomes sharp with movement.
• Swelling or fullness in the sinus tarsi region, sometimes mistaken for a cyst.
• Instability, especially on uneven ground.
• Pain with inversion or eversion, due to subtalar joint irritation.
• Tenderness on palpation of the sinus tarsi.
• Difficulty with prolonged standing, walking, or sport.

Symptoms often worsen with:

• uneven surfaces
• quick directional changes
• prolonged weight?bearing

A hallmark diagnostic clue is pain relief after local anesthetic injection into the sinus tarsi

Pathophysiology

Sinus tarsi syndrome involves:

• Synovitis of the subtalar joint
• Hemorrhage or inflammation of sinus tarsi fat pads
• Ligament tears, especially the interosseous talocalcaneal ligament
• Scar tissue formation after repeated sprains
• Subtalar instability, altering joint mechanics and increasing shear forces

MRI often shows replacement of normal sinus tarsi fat with fluid or scar tissue, and may reveal ligament disruption or ganglion cysts.

Diagnosis

Diagnosis is primarily clinical but supported by imaging:

• X?ray — may show subtalar joint osteoarthritis or impingement in chronic cases.
• CT — detects early bony changes.
• MRI — best for soft?tissue evaluation; identifies inflammation, ligament injury, or cysts.
• Bone scan — highlights subtalar inflammation.
• Diagnostic injection — confirms the sinus tarsi as the pain source.

Differential diagnoses include peroneal tendinopathy, anterior ankle impingement, and subtalar arthritis.

Management Strategies

1. Conservative Treatment (First?line)

Conservative care is effective for most patients.

• Activity modification — reduce hills, uneven surfaces, and high?impact activities.
• Immobilization — short?term bracing or boot use to reduce inflammation.
• Anti?inflammatory medication — NSAIDs for pain and swelling.
• Physical therapy —
  • peroneal strengthening
  • calf and intrinsic foot muscle training
  • proprioception and balance retraining
  • subtalar joint mobilization
• Orthotics — helpful for pronation or flatfoot?related Sinus tarsi syndrome.
• Footwear modification — supportive shoes, lateral posting, or stability footwear.

2. Injections

• Corticosteroid injections may provide short?term relief but symptoms can recur.
• Local anesthetic injections aid diagnosis and temporary pain relief.

3. Surgical Treatment

Surgery is rarely required. When conservative care fails:

• Arthroscopic debridement — removes scar tissue or inflamed synovium.
• Ligament reconstruction — for persistent subtalar instability.

Surgical outcomes are generally favorable but reserved for chronic, refractory cases.

Prognosis

Most patients improve significantly with structured rehabilitation and biomechanical correction. Conservative treatment is usually successful, and surgery is uncommon.

However, prognosis depends on:

• severity of ligament injury
• presence of chronic instability
• adherence to rehabilitation
• underlying foot mechanics

Early diagnosis and treatment reduce the risk of chronic pain and recurrent instability.

Sinus tarsi syndrome is a multifactorial condition characterized by lateral hindfoot pain, instability, and inflammation within the sinus tarsi. Most commonly triggered by ankle sprains, it involves a combination of ligament injury, synovitis, and altered subtalar mechanics. Diagnosis relies on clinical examination supported by imaging, particularly MRI. Conservative management—including physical therapy, orthotics, and activity modification—is effective for most individuals, while surgery is reserved for persistent cases.

Understanding the interplay between ankle stability, subtalar mechanics, and foot posture is essential for effective treatment and long?term recovery.